Why is my viewport frame rate so slow?
One of the problems with blender right now when using particles system is that it is not easy (or nearly impossible) to make the instances avoid each other and not overlap, and thus cover maximum space.
You Setup is great, I'm thinking that you have too much grass in your scene, probably more than you need to cover the surface. If you show me a screenshot of your scene or your particles settings at least, I can pinpoint (and I will update this answer accordingly).
PS: Also, just a friendly tip, yes Graswald is a good add-on, but do consider checking out Scatter add-on
https://www.blendernation.com/2020/04/03/blender-add-on-spotlight-scatter/
disclaimer: I'm in no way related to devs of either add-ons. So this recommendation is purely professional, unbiased.